The objective of this research program is to elucidate biochemically and morphologically the fundamental lesion(s) of pulmonary oxygen toxicity in the newborn and to characterize and measure the development and progressson of this lesion(s) and its sequelae so that agents potentially capable of ameliorating or preventing the acute and chronic damage to the lung can be rigorously evaluated. It is proposed: (1) to determine when the newborn mouse becomes "adult" in its mortality response to continuous exposure to 100% oxygen and to characterize the mileu that exists at that time, (2) to expand the evaluation and quantitation of the reactive changes in specific cell types of the newborn lung resulting from exposure to 100% oxygen, (3) to quantitate the changes in interstitial tissue, bronchioles, small blood vessels, and scar tissue in the newborn mouse lung exposed to 100% oxygen, (4) to measure the effect of superoxide dismutase and antioxidant drugs capable of protecting against the effects of pulmonary oxygen toxicity at normal atmospheric pressure, (5) to continue to measure biochemically and evaluate morphologically the parameters indicating the completeness of recovery from exposure to 80-100% oxygen in the growing newborn lung, (6) to continue to measure biochemically and evaluate morphologically the effect on the growing lung of exposure to oxygen concentrations below 100% for prolonged periods of time.